The present invention relates to apparatus for monitoring uterine contractions during pregnancy and throughout labor and delivery. Information relating to the frequency, magnitude and pattern of such contractions is valuable to the physician, as a measure of the normal progression of labor. Additionally, it provides a guide for nurses and physicians in the use of medication or the need for other remedial actions.
The two types of apparatus most widely used at the present time for monitoring labor contractions are: (1) internal catheters inserted into the uterus to measure changes in the amniotic fluid pressure in the amniotic sac such as generally shown in the Pack U.S. Pat. No. 4,543,965; and (2) external devices which consists of a pressure transducer held in place on the abdomen of the patient by a belt fitted around the waist of the patient such as generally shown in the Fuzzell U.S. Pat. No. 3,520,294.
The most reliable device is the internal type. This means for measuring uterine contractions usually provides accurate data, but has a number of significant disadvantages which include:
1. The uterine cervix must be partially dilated and the amniotic sac ruptured.
2. During insertion of the catheter, bacterial and/or viral contaminants may be carried from the vagina and/or cervix into the uterine cavity and cause serious infection.
3. The catheter system may not be used where certain complications exist, e.g. uterine bleeding, here catheter insertion might cause additional bleeding; fever due to suspected uterine infection, in this case catheter insertion might exacerbate the situation.
4. If great care is not taken, during insertion of the catheter through its guiding tube, the lower segment of the uterus may be perforated.
5. Catheter insertion is uncomfortable for the patient and inconvenient and time consuming for the medical and nursing staff. Before insertion a sterile area must be prepared around the vaginal orifice and then draped with sterile towels. The catheter, catheter guide, fluid filled syringe and pressure measuring apparatus then have to be assembled. The entire operation usually takes 7-10 minutes.
6. Even though great care is exercised during catheter insertion, it is possible for the catheter to become clogged with a blood clot or vernix caseosa during labor so that the recorded uterine contraction data is compromised, sometimes to the point where it is not usable, even though the catheter system has been flushed with sterile water. In this case, the catheter must be replaced and the entire insertion process repeated.
7. During attempted flushing it is possible to damage the expensive pressure transducer if the flushing fluid is inadvertently directed towards the pressure transducer rather than towards the catheter.
8. Uterine contractions are often not monitored in the delivery room because current catheter systems usually place the pressure transducer directly on the fetal monitor so that patient transfer from labor to delivery room requires the reconnection of the catheter system to another pressure transducer on another fetal monitor--an awkward and time-consuming process. Additionally, it is difficult to maintain catheter sterility during the transfer process.
The external type of apparatus presently used consists of a pressure transducer held in place against the patient's abdomen by an encircling belt. The belt provides the counter-pressure which keeps the pressure transducer firmly against the maternal abdominal wall during contractions. Without it, the pressure transducer would merely ride up and down with each uterine contraction and hence would not reflect the changes in abdominal wall tension associated with uterine contractions.
While the external system is simple and convenient to use and does not suffer from some of the major disadvantages of the internal system, it too has significant problems, which include:
1. Even under the best of conditions the overall quality of data obtained by external means is not as precise as that obtained using an internal uterine catheter.
2. Uterine contraction data is easily compromised by fluctuations in belt tension. If the labor is intense and the patient moves, belt tension changes continually. Hence for satisfactory operation, the patient must be kept relatively immobile. Once belt tension has been altered by patient movement, the belt tension must be readjusted, otherwise no uterine activity data will be recovered.
3. When the patient is transferred from the labor ward to the delivery room the belt tension has to be readjusted. Because this can be time consuming, it is not usually done so that the external technique is infrequently used in the delivery room.
4. Because of the foregoing problems, current external uterine activity monitoring techniques provide at the best a fragmentary record of activity, even so, much of the data is of poor quality.
In the past, means other than a belt for fixing the external transducer to the patient's abdomen have been attempted.
As long ago as 1932 in "Surgery, Gynecology and Obstetrics," Vol. 55 (1932) at page 45, a tripod support assembly was disclosed which had an air transducer supported in a tripod-like structure which was fixed by tapes tied in ringlets of the tripod which was held fast by adhesive straps to the patient's loins. This structure was not widely employed and is not presently being used. In effect, this system conceptually was a precursor of the belt system.
Another prior art device disclosed in "Science-1947" at page 427 (shown diagramatically in FIG. 6) consisted of a heavy brass ring (240 grams) held in place on the abdomen by double coated Scotch brand adhesive tape applied to the bottom side. A strain gauge is held in the center of each ring by a single lever system. This system was devised by Dr. Reynolds, but has never been widely used and is not in use at the present time.
The Reynolds device used doubled-sided adhesive tape to prevent lateral movement of the rings. The weight of the rings provided counter-pressure to hold the strain gauge against the abdomen during episodic changes in abdominal wall tension which occurs with uterine contractions. Since the operation of the device depended on gravitational forces to hold the strain gauge in correct relationship to the abdominal wall, it was mandatory that the patient be on her back and be relatively immobile during the use of the device.
Because of the disadvantages of the external uterine contraction devices, the internal catheter system is considered the method of choice when accurate uterine contraction data is necessary for patient management.